Patients with desmosterolosis carry high levels of cholesterol precursor desmosterol in plasma, tissue, and cultured cells, caused by the deficiency of the enzyme 3β-hydroxysterol Δ24-reductase (DHCR24), which catalyzes the reduction of the Δ24 double bond of sterol intermediates in cholesterol biosynthesis. This evidence concerns the gene DHCR24 and desmosterolosis.